The development of productive and economical methods for the fermentation of antibiotic-producing microorganisms presents substantial problems to the microbiologist, the chemist and the engineer. The problems associated with the large-scale production of antibiotics are often complicated when the microorganism produces multiple antibiotic factors that are closely related to each other in chemical and physical characteristics. Such a complex or mixture of antibiotic factors renders the isolation of a particular desired antibiotic factor difficult.
Attempts to produce a desired antibiotic factor to the exclusion or near exclusion of other co-produced factors have generally involved two approaches. One approach has been to control production of co-produced factors or components by shifting the ratio or choice of substrates employed in the fermentation and varying the physical environment of the antibiotic-producing microorganism by altering the temperature, pH, aeration, agitation, length of fermentation time, etc. A significant problem in trying to effect control of biosynthesis with such changes in the environment is that full control is seldom truly achieved and small fluctuations in the physical parameters may produce unpredictable results.
The second approach employed in seeking to produce a predominance of a single desired factor in a fermentation which normally produces multiple factors has been to develop a strain of the antibiotic-producing organism that will biosynthesize the desired antibiotic in greater abundance. The development of such a strain commonly involves the empirical method of strain selection. A method frequently employed for strain selection involves the treatment of a culture with a mutagen and randomly selecting isolated colonies for examination of their capability for producing the desired antibiotic. Difficulty is frequently encountered with this latter approach since the selected strain is often found to be unstable.
One example of an antibiotic fermentation in which multiple factors are produced is that which produces the new broad spectrum antibiotic nebramycin by culturing Streptomyces tenebrarius ATCC 17920 under submerged aerobic fermentation conditions, U.S. Pat. No. 3,691,279; Stark, W. M., Hoehn, M. M., Knox, N. G., Antimicrobial Agents and Chemotherapy -1967, p. 314-323; Thompson, R. Q., Presti, E. A., ibid, p. 332-340. Eight closely related antibiotic components have been separated from the nebramycin complex and have been identified by paper chromatography bioautographs. All components in the complex are basic, water-soluble compounds that are in the general class of aminoglycosidic antibiotics such as gentamicin, kanamycin, neomycin and others.
All of the major components of the nebramycin complex in the current process exhibit excellent antibiotic activity against gram-negative bacilli and staphylococci. Wick, W. E. and Welles, J. S., Antimibcrobial Agents and Chemotherapy -1967. p. 341-348. However, nebramycin factor II is of particular importance because of its antibiotic activity against Pseudomonas species.
The isolation of each factor as a pure compound from the nebramycin complex is a time-comsuming process which requires extensive column chromatography. A production process yielding only the single nebramycin component, factor II, (hereinafter nebramycin II) rather than the complex of antibiotics, would provide a more economical and desirable process for the production of nebramycin II.
It is an object of this invention to provide an improved process for the production of nebramycin II. In particular it is an object of this invention to provide an improved fermentation process for the production of nebramycin II essentially free of other antibiotic factors and thereby render the isolation of nebramycin II from the fermentation medium economically advantageous. It is a further object of this invention to provide the new nebramycin antibiotic factor, nebramycin VII.